Examination of gas transport through polysiloxane open cell foams: Effects of compression upon model flow, permeation parameters, and cell morphology

A study to test a model for gas flow through a polymer foam system was conducted. The goal was to quantitatively relate polymer foam compression and gas pressure drop across the specimen, to the gas flow through the foam. Foam cell morphology was studied to assess adequacy of the model to accommodate material characteristics.; X-ray tomographic images were collected for polydimethylsiloxane (PDMS) foam material under various levels of compression. The intent was to implement a systematic analysis method of correlating some aspect of these images to the cell morphology in order to enhance understanding of the material characteristics. It was shown that x-ray tomography is a useful nondestructive method for understanding the compressive behavior of a mechanically loaded polymer foam. As a general trend, the experimentally obtained x-ray attenuation coefficient could be correlated with the effective density of the polymer foam, approaching values for the polymer resin as foam compression increased. Mechanical properties of the cellular polymer could also be elucidated.; Experimental data was collected for several gas flow rates in the free molecular flow regime, for foam compressions ranging from 0 to 40%. For each experiment, data for temperature, incoming pressure (p_in), and pressure drop (Δp) were compiled and used to calculate foam permeability. Permeability demonstrated a linear dependence on the gas flow rate, but an exponential dependence upon the degree of compression.; Logarithmic plots of steady-state pressure drop, Δp, and time required to reach steady-state, t_ss, provided more information about gas flow through the foam. Regression analysis was used to predict flow behavior at higher compressions.; A model correction must be included for the percolation behavior displayed by the foam material under study, since flow is occluded at a compression of 33% (0.22 porosity). This decrease in flow at a critical porosity is a disruption of the original model equations, which did not allow for the critical percolation threshold. Additionally, a term that characterizes permeation through the solid polymer can describe flow behavior at compressions where open cell flow paths are blocked.